[sdiy] current mirror for NPN expo?

[Dan Snazelle]

I loved reading all about your ARIES!

Thanks


I got my dual VCO to work by adding a small resistance AND by sorting through transistors....the transistor is crucial


Thanks all!

Sent from my iPhone

On Sep 19, 2011, at 11:53 PM, "Dave Brown" <davebr at earthlink.net> wrote:

> The Aries 317 module I just repaired did just this with a current mirror for
> two VCOs.  The main VCO generates the triangle wave with the derivative sine
> and square waves.  The secondary VCO generates the saw waveform.  They reset
> the saw waveform from the square and added the 10R in the second current
> mirror to adjust the saw amplitude.  The upside is a great set of waveforms
> with no glitches.  The downside is the saw amplitude does vary a bit over
> the range.  I have waveform images on my 317 repair page.
> http://modularsynthesis.com/aries/AR-317/ar-317.htm
> 
> Dave
> 
> -----Original Message-----
> From: synth-diy-bounces at dropmix.xs4all.nl
> [mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of David G Dixon
> Sent: Monday, September 19, 2011 11:41 AM
> To: 'Harry Bissell'; 'dan snazelle'
> Cc: 'synthdiy diy'
> Subject: Re: [sdiy] current mirror for NPN expo?
> 
> yeah, this "driving two VCOs from one expo" idea is a non-starter, I'd say. 
> 
>> -----Original Message-----
>> From: Harry Bissell [mailto:harrybissell at wowway.com]
>> Sent: Monday, September 19, 2011 9:56 AM
>> To: dan snazelle
>> Cc: David G Dixon; synthdiy diy
>> Subject: Re: [sdiy] current mirror for NPN expo?
>> 
>> that is a different issue... I'd expect that the additional core must 
>> have its timing capacitor closely matched to the first, not at all 
>> easy to do...
>> 
>> H^) harry
>> 
>> 
>> ----- Original Message -----
>> From: dan snazelle <subjectivity at hotmail.com>
>> To: David G Dixon <dixon at mail.ubc.ca>, synthdiy diy 
>> <synth-diy at dropmix.xs4all.nl>
>> Sent: Mon, 19 Sep 2011 12:40:12 -0400 (EDT)
>> Subject: Re: [sdiy] current mirror for NPN expo?
>> 
>> that is how i ended up trying it...however the pitch is not exactly 
>> the same on the second core...even though the part values are the 
>> same...i will keep working at it
>> 
>> thanks
>> 
>> On Sep 19, 2011, at 12:15 PM, David G Dixon wrote:
>> 
>>>> can anyone point me towards info on how to use ONE NPN
>> EXPO to drive two vcos?
>>> 
>>> Can't you just mirror the current-sourcing one?  I.e., tie
>> its emitter
>>> to the other two, and connect its base to the other
>> current-sourcing
>>> one?  You should be able to replicate the current as many
>> times as you want this way.
>>> I did it with five transistors in a four-pole filter once;
>> it worked a
>>> treat.
> 
> 
> 
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